creeps
To mime is to act out silently.
silently
The word silently *is* an adverb. The adjective form is "silent."
The word is silentium.
more silently
in condert
Silently is an adverb. Many adverbs end in the prefix -LY.
cheeky
Noisily
It is neither. The word silently is an adverb, the adverb form of the adjective silent.
Yes, it is the adverb form of the adjective silent.
The word silently, like most (but not all) words that end in -ly, is an adverb.